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Elimination

The first step is to make the structure as flyproof as possible by putting up screens or by caulking wherever the flies come in. Then spray liquid insecticide outside at strategic spots along the walls. This must be done by a professional toward mid-August before the flies start to work their way indoors.

It can also help to put sticky traps near windows and light sources. Pyrethrin-based aerosols like Maheu&Maheu Flying Insect Killer can also lend a hand given their very fast-acting effect. You can also apply Maheu&Maheu Crawling Insect Killer around windows because that is where the flies tend to cluster.

Maheu&Maheu Insecticide Dust is recommended for the attic and other hollow spaces, which are popular hiding places for the flies. Remember, however, that it is very important to vacuum up any dead flies because they can attract other pests, like the Larder Beetle.

Actions

  • Spray or treat entry points on the outside walls of the house with an insecticide labeled for this use
  • Spray or treat the perimeters of rooms and around window frames with an insecticide

Prevention

  • Seal the outsides of windows, doors, eaves, chimneys, etc. as completely as possible

Description and development

The Cluster Fly (Pollenia rudis F. ) is a holometabolous insect of the Diptera order and the Calliphoridae family. It is bigger (8 to 10 mm) than the House Fly and other flies encountered indoors. Its thorax is dark gray, and young adults have yellowish or golden hairs like the color of pollen, which explains their Latin name. At rest, the Cluster Fly’s wings fold over each other and the fly’s back. When squashed, these flies emit a smell similar to buckwheat honey.
Cluster Flies are frequent pests in homes and commercial buildings, where they hibernate from fall to spring. Each spring when the ground thaws and grass starts to grow, the flies leave their winter refuge to breed, laying eggs one by one in the ground. Larvae emerge from the eggs three days later, burrow into the ground, and penetrate an earthworm to feed. Once they have finished growing (after 13 to 22 days), they emerge from the ground and turn into pupae. The pupal stage lasts 11 to 14 days, which brings the total life cycle to about 33 days. There can be 3 or 4 generations per summer, depending on soil humidity, temperature, and other conditions.

Habits

These flies usually live outside, where they feed off flowers, fruit, and sometimes tree sap. When seeking shelter for the winter, they can fly distances of more than 2 km. They congregate in great numbers in the walls of selected buildings with the greatest sun exposure. They get inside through structural defects and other available openings. Once there, they cluster together in attics, walls, and other hollow spaces in the structure, which is why they are called Cluster Flies.

These flies are easy to tell apart from House Flies by their behavior. They are very attracted to ultraviolet sunlight and often buzz around in windows. An ordinary electric light can also attract them-they can flit for hours around a lampshade or fluorescent lights.

Their behavior is unpredictable. Sometimes they will walk right on your face and fall into your coffee mug for no apparent reason. Fortunately, they do not breed indoors. In nature they hibernate in hollow trees under the bark as well as in rock crevices.

In colder rooms, these flies can remain dormant right until spring. However, those that have taken refuge in warmer spots can emerge at any point during the winter and cluster in the windows. Between spring and fall, they spend all their time outdoors.

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